Methods and compositions for polyurethane dispersions using caprolactam-derived solvents

ABSTRACT

Caprolactam-derived solvents for use as processing solvents and/or coalescing agents for polyurethane dispersions (PUDs). The caprolactam-derived solvents are suitable for processing solvents and coalescing agents in PUDs created through traditional PUD manufacturing processes or as coalescing agents in PUDs created through solvent-free PUD manufacturing processes. Blends of more than one caprolactam-derived solvent may be used as the processing solvent and/or coalescing agent.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 16/611,384, filed Nov. 6, 2019, which is a U.S. 371National Stage Application of International Application No.PCT/US2018/038924, filed Jun. 22, 2018, which claims the benefit underTitle 35, U.S.C. § 119(e) of U.S. Provisional Patent Application Ser.No. 62/524,786, entitled METHODS AND COMPOSITIONS FOR POLYURETHANEDISPERSIONS USING CAPROLACTAM-DERIVED SOLVENTS, filed on Jun. 26, 2017,and of U.S. Provisional Patent Application Ser. No. 62/579,636, METHODSAND COMPOSITIONS FOR POLYURETHANE DISPERSIONS USING CAPROLACTAM-DERIVEDSOLVENTS, filed on Oct. 31, 2017, the entire disclosures of which areexpressly incorporated by reference herein.

FIELD

The present disclosure relates to solvents for the preparation and/oruse of polyurethane dispersions and, in particular, tocaprolactam-derived solvents for use as processing solvents and/orcoalescing agents in polyurethane dispersions.

BACKGROUND

Polyurethane dispersions (PUDs) were developed several decades ago toaddress the increasing environmental demands on the adhesive industry toproduce adhesives containing little or no solvents. In more recentyears, PUDs have been used as coatings, adhesives, sealants, andelastomers, among other applications. PUDs are aqueous, anionicdispersions of high molecular weight polyurethanes, and offer thebenefits of polyurethane polymers, such as toughness and scratch andchemical resistance, for a wide range of applications.

In general, PUDs are manufactured through one of two processes. A firstprocess, referred to herein as the traditional PUD manufacturingprocess, includes first making a pre-polymer through a reaction betweena polymeric diol, diisocyanate, and a hydrophilic agent in the presenceof a processing solvent. The free acid group in the hydrophilic agentenhances the resin water solubility or dispersibility afterneutralization with a base, preferably a nitrogen containing base.

However, production of PUD pre-polymers, especially those with lowmolecular weight and high solids, requires high amounts of processingsolvents to control viscosity. N-alkyl pyrrolidones, especially N-methyl(NMP), N-ethyl (NEP), N-butyl (NBP) and other alkyl pyrrolidones, havebeen used as the processing solvents for many years. However, there issignificant regulatory pressure to eliminate the use of N-alkylpyrrolidones and other solvents due to toxicity concerns. For example,NMP and NEP have been classified as reproductive toxicity category 1B inEurope (European Commission Regulation (EC) No. 1272/2008 (CLP) and (EU)No. 944/2013, respectively, on Dec. 19, 2016), and NMP and similarchemical substances are currently under initial risk evaluation in theUnited States. As such, PUD producers have been in search of a suitablereplacement for NMP. In recent years, one existing class of solvents foruse in the traditional PUD manufacturing process include potentiallyless toxic NMP derivatives, such as those disclosed in U.S. PatentApplication Publication No. 2015/0057375 to Vandeputte et al.

One alternative to using pyrrolidone based solvents includes usingacetone or mixtures of acetone and/or methylethyl ketone (MEK) (see U.S.Pat. No. 4,820,762 to Tsaur) in place of NMP, for the manufacturing ofPUDs. This process, referred to herein as a solvent-free PUDmanufacturing process, includes the step of removing processing solventsprior to formulating the final dispersion product and, for this reason,the method is considered “solvent-free.”

However, these solvent-free based processes are not free ofdisadvantages. For instance, copious amounts of MEK or acetone aretypically required to attain a desired viscosity low enough for thepre-polymer such that the operation requires larger reaction andprocessing containers making these types of processes complex andexpensive. In addition, since these solvents are not coalescing agents,they must be removed completely after making the polyurethane dispersioncomposition and prior to sale and/or application. Furthermore, the mostcommonly used hydrophilic agent for the production of the PUD resin,dimethylol propionic acid (DMPA), is not compatible with acetone andMEK, which have been used to replace NMP. As a result, the use ofacetone and/or MEK solvents required the use of an expensive hydrophilicagent, dimethylolbutanoic acid (DMBA), which is compatible with suchsolvents. However, DMBA is significantly more expensive than DMPA.Another drawback to previous methods of formulating PUDs is the presenceof residual solvents in the PUD resin which negatively impacts the filmforming step in the dispersions. Thus, the customer or end-user has toadd coalescing agents in order to achieve the coalescing effect, whichadds cost.

In order to avoid the complex ‘acetone’ process, a ‘melt’ process may beused, in which the polyols, polyisocyanates and hydrophilic acidcomponents are reacted without the use of any solvent. In this process,the chain extension step is completed after the neutralization anddispersion steps to avoid viscosity buildup. However, this ‘melt’process suffers from high viscosities during the production of PUDresins and is not suitable for all the different types of polyols andpolyisocyanates for yielding various types of PUD resin chain backbones.

In another process directed to avoid using N-alkyl pyrrolidones orketones, monomers instead of polyols are reacted with polyisocyanatesand hydrophilic agents to produce PUD resins. In this process, themonomers act as the solvent to enable controlling the viscosity duringthe process. One example is the use of acrylic monomers(acrylic/methacrylic acids and esters) for the production of PUDs. Thistype of process is complex and is only applied to acrylic modified PUDsand cannot be applicable to other polyol systems such as polyether,polyester, alkyd, polycarbonate (see U.S. Pat. No. 8,859,676), andpolyamide, for example.

In other versions of PUDs, polyisocyanates having partially blockedisocyanate groups are used to produce “blocked PUD” systems, which maybe used to modify the characteristics of the coating or paint such thata bake cure is required. Such blocked PUDs can be produced by partiallyblocking the polyurethane pre-polymer, made from polyols,polyisocyanates and a hydrophilic agent, by adding a blocking agent insuch quantity that only a portion of the isocyanate groups in thepre-polymer are blocked. The remaining isocyanate groups enable thesubsequent chain extension step for the production of PUDs. In anotherprocess, partially blocked polyisocyanates (HDI Trimer, IPDI Trimer) areused in the preparation of the pre-polymer. The preparation of blockedor partially blocked PUD systems is well known and described further inU.S. Pat. Nos. 4,098,933, 4,835,210, 5,157,074, 7,589,148 and 8,859,676.Controlling the viscosity during the preparation of such partiallyblocked PUD pre-polymer is even more critical due to the presence ofisocyanate moieties from the blocked polyisocyanates.

Thus, what is needed are solvents that are inert and non-reactive (todiisocyanate), compatible with hydrophilic agents, hydrolytically stableover a broad pH range, offer good viscosity control of the PUD resin,are non-toxic and have high solvating power, a moderate evaporationrate, and low odor.

SUMMARY

The present disclosure provides caprolactam-derived solvents suitablefor use as processing solvents and/or coalescing agents in polyurethanedispersions (PUDs). More particularly, the caprolactam-derived solventsare suitable for use as processing solvents and coalescing agents inPUDs created through traditional PUD manufacturing processes or ascoalescing agents in PUD dispersions created through solvent-free PUDmanufacturing processes. Also, blends of more than onecaprolactam-derived solvent may be used as the processing solvent and/orcoalescing agent.

In one form thereof, the present disclosure provides a method of forminga polyurethane dispersion including the steps of: forming a pre-polymerfrom a polymeric diol, at least one of a polyisocyanate and adiisocyanate, and a hydrophilic agent dissolved in at least one solvent,the at least one solvent in the form of a caprolactam derivative of theformula:

where R is a 1-5 carbon unsubstituted or substituted alkyl group; addingat least one base to the pre-polymer; and dispersing the pre-polymer inwater.

The alkyl group may be selected from methyl, ethyl, propyl, iso-propyl,butyl, iso-butyl, and a substituted alkyl.

In the method, at least one of the following conditions may be present:the at least one base is an amine; the polymeric diol includes at leastone polymeric diol selected from a polyether polyol, a polyester polyol,a polycarbonate polyol, a polyamide polyol, an acrylic polyol andcombinations thereof; the at least one of the polyisocyanate and thediisocyanate is diisocyanate, which includes at least one diisocyanateselected from a aliphatic diisocyanate and an aromatic diisocyanate andcombinations thereof; and the hydrophilic agent is selected from thegroup consisting of dimethylol propionic acid, dimethylol butanoic acid,and combinations thereof.

The at least one solvent may include a blend of at least two of N-methylcaprolactam, N-ethyl caprolactam, and N-butyl caprolactam.

The blend may include a first solvent in a range of 25-75 wt. %, and asecond solvent in a range of 75-25 wt. %, based on the combined weightof the first and second solvents. The first solvent may be N-methylcaprolactam, and the second solvent may be N-ethyl caprolactam. Theblend may include about 50 wt. % of N-methyl caprolactam and about 50wt. % N-ethyl caprolactam %, based on the combined weight of the firstand second solvents.

The blend may include a first solvent and a second solvent, a ratiobetween the first solvent and the second solvent being one of 2:1, 1:1,or 1:2.

The method may further include the step of using a blocking agent to atleast partially block the pre-polymer.

In another form thereof, the present disclosure provides a polyurethanedispersion composition including a polyurethane formed of a polymericdiol, at least one of a polyisocyanate and a diisocyanate, and ahydrophilic agent dispersed in a solution of water and one of acaprolactam-derived N-alkyl solvent and an open chain ester amide.

The caprolactam-derived N-alkyl solvent may be of the formula

and the open chain ester amide may be of the formula

wherein n=0 or 1, R₁ is H or methyl, and R and R₂ are each a 1-5 carbonunsubstituted or substituted alkyl group selected from methyl, ethyl,propyl, iso-propyl, butyl, and iso-butyl.

In the polyurethane dispersion composition, the alkyl group may be oneof methyl, ethyl, propyl, iso-propyl, butyl, iso-butyl and a substitutedalkyl.

In the polyurethane dispersion composition, the one of thecaprolactam-derived N-alkyl solvent and the open chain ester amide mayconstitute between about 1 wt. % and about 10 wt. % of the dispersion.In the polyurethane dispersion composition, the one of thecaprolactam-derived N-alkyl solvent and the open chain ester amide mayconstitute between about 3 wt. % and about 6 wt. % of the composition.

In another form thereof, the present disclosure provides a method offorming a polyurethane dispersion including the steps of: forming apre-polymer from a polymeric diol, at least one of a polyisocyanate anda diisocyanate, and a hydrophilic agent dissolved in at least oneprocessing solvent; adding at least one base to the pre-polymer;dispersing the pre-polymer in water; removing the processing solventfrom the polyurethane dispersion; adding a coalescing agent to thepolyurethane dispersion, the coalescing agent being in the form of oneof the formulas:

wherein n=0 or 1, R₁ is H or methyl, and R and R₂ are each a 1-5 carbonunsubstituted or substituted alkyl group selected from methyl, ethyl,propyl, iso-propyl, butyl, and iso-butyl.

The alkyl group may be selected from methyl, ethyl, propyl, iso-propyl,butyl, iso-butyl, and a substituted alkyl. The alkyl group may bemethyl. The alkyl group may be ethyl.

In the method, at least one of the following conditions may be present:the processing solvent is selected from acetone and methyl ethyl ketoneand combinations thereof; the at least one base is an amine; thepolymeric diol includes at least one polymeric diol selected from apolyether polyol, a polyester polyol, a polycarbonate polyol, apolyamide polyol, an acrylic polyol and combinations thereof; the atleast one of the polyisocyanate and the diisocyanate is diisocyanate,which includes at least one diisocyanate selected from a aliphaticdiisocyanate and an aromatic diisocyanate and combinations thereof; andthe hydrophilic agent is selected from the group consisting ofdimethylol propionic acid, dimethylol butanoic acid, and combinationsthereof, wherein when the processing solvent is selected from acetoneand methyl ethyl ketone and combinations thereof, the hydrophilic agentis dimethyl butanoic acid.

The method may further include the step of using a blocking agent to atleast partially block the pre-polymer.

As used herein, the phrase “within any range defined between any two ofthe foregoing values” literally means that any range may be selectedfrom any two of the values listed prior to such phrase regardless ofwhether the values are in the lower part of the listing or in the higherpart of the listing. For example, a pair of values may be selected fromtwo lower values, two higher values, or a lower value and a highervalue.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned and other features of the disclosure, and the mannerof attaining them, will become more apparent and the disclosure itselfwill be better understood by reference to the following description ofembodiments of the disclosure taken in conjunction with the accompanyingdrawings.

FIG. 1 is a diagram of a traditional PUD manufacturing process.

FIG. 2 is a diagram of a solvent-free PUD manufacturing process.

FIG. 3 a is a diagram of a traditional PUD manufacturing processincluding introduction of a blocking agent to a pre-polymer to produce ablocked PUD.

FIG. 3 b is a diagram of a solvent-free PUD manufacturing processincluding introduction of a blocking agent to a pre-polymer to produce asolvent-free blocked PUD.

FIG. 4 a is a diagram of a traditional PUD manufacturing processincluding introduction of a blocked isocyanate to produce a blocked PUD.

FIG. 4 b is a diagram of a solvent-free PUD manufacturing processincluding introduction of a blocked isocyanate to produce a solvent-freeblocked PUD.

FIG. 5 corresponds to Example 3, and is a graph of storage stability andviscosities for various coalescing agents.

FIG. 6 corresponds to Example 3, and is a graph of open times forvarious coalescing agents.

FIG. 7 corresponds to Example 3, and is a graph of drying times forvarious coalescing agents.

FIG. 8 corresponds to Example 3, and illustrates freeze-thaw stabilityand film properties for ester alcohol, NBP, N-methyl caprolactam (NMCPL), NMP, and N-ethyl caprolactam (NE CPL).

FIG. 9 corresponds to Example 3, and illustrates freeze-thaw stabilityand film properties of N-methyl caprolactam (NM CPL), 1:1 NM CPL:NE CPL,2:1 NM CPL:NE CPL, and 1:2 NM CPL:NE CPL after being subject to fivefreeze-thaw cycles.

Corresponding reference characters indicate corresponding partsthroughout the several views. Although the drawings representembodiments of various features and components according to the presentdisclosure, the drawings are not necessarily to scale and certainfeatures may be exaggerated in order to better illustrate and explainthe present disclosure. The exemplifications set out herein illustrateone or more embodiment of the disclosure, and such exemplifications arenot to be construed as limiting the scope of the disclosure in anymanner.

DETAILED DESCRIPTION

The present disclosure provides caprolactam-derived solvents suitablefor use as processing solvents and/or coalescing agents in PUDdispersions. More particularly, the caprolactam-derived solvents aresuitable for processing solvents and coalescing agents in PUDdispersions created through traditional PUD manufacturing processes oras coalescing agents in PUD dispersions created through solvent-free PUDmanufacturing processes.

I. Caprolactam-Derived Solvents.

Solvents of the present disclosure may be derived from caprolactam, andhave one of the following general formulas (I) or (II):

wherein n=0 or 1, R₁ is H or methyl, and R and R₂ are each a 1-5 carbonunsubstituted or substituted alkyl group, including methyl, ethyl,propyl, iso-propyl, butyl, or iso-butyl or a substituted alkyl groupincluding a cyano, nitro, nitroso, formyl, or other polar substitute,such as 2-cyano ethyl. R₂ may also be benzyl. In one embodiment, n=0 andR₁ is methyl. In another embodiment, n=1 and R₁ is hydrogen.

As discussed further below, the solvents of the present disclosure maybe used as processing solvents in the production of polyurethanepre-polymers and/or as coalescing agents in polyurethane dispersions.

There are several processes for the preparation of caprolactam-derivedsolvents (e.g. German Patent DE 2025172, German Patent DE 3735904,Romania Patent RO 102421, U.S. Pat. Nos. 3,865,814, 5,338,861,“N-Alkylation of Lactams with Phase Transfer Catalyst” by Takahata etal., HeteroCycles: An International Journal for Reviews andCommunications in Heterocyclic Chemistry, 1979, Vol. 12, No. 11, pp.1449-51, and “N-Substituted Derivatives of ε-caprolactam and TheirThermal and Chemical Behavior” by Cuiban et al., ARKIVOC Journal, Vol.2002, Part (ii), pp. 56-63). One such method involves deprotonation ofthe amide group with a base such as sodium hydride or sodium metal,followed by alkylation with alkylation agents such as alkyl halides,dialkyl sulfates, or alkyl tosylates/acetates, followed by an aqueousworkup to remove the byproducts. As one example, when the alkyl group onthe caprolactam-derived solvent is 2-cyano ethyl, acrylonitrile is thepreferred choice of alkylating agent.

There are also several methods for the preparation of solvents havingopen chain ester amides. One method involves cyclic imides such as2-methylglutarimide or adipimide that are ring opened by means ofalcohols followed by trans dialkylamidation. Another method involvestransamidation of dialkyladipate or adipic acid mono acid chloride withdialkyl amine (e.g. PCT Patent Application Publication No. WO2009/056477).

In various embodiments, the caprolactam-derived solvents may be usedindividually or two or more of the caprolactam-derived solvents may beblended together.

For example, in some embodiments, a caprolactam-derived solvent of thepresent disclosure may be a blended solvent composition including firstand second different caprolactam-derived solvents. The first solvent maybe present in an amount as little as 15 wt. %, 25 wt. %, 35 wt. %, or asgreat as 65 wt. %, 75 wt. %, or 85 wt. %, based on the total weight ofthe first and second solvents, or may be present in an amount within anyrange defined between any two of the foregoing values, such as between15 wt. % and 85 wt. %, between 25 wt. % and 75 wt. %, or between 35 wt.% and 65 wt. %, for example.

The second solvent may also be present in an amount as little as 15 wt.%, 25 wt. %, 35 wt. %, or as great as 65 wt. %, 75 wt. %, or 85 wt. %,based on the total weight of the first and second solvents, or may bepresent in an amount within any range defined between any two of theforegoing values, such as between 15 wt. % and 85 wt. %, between 25 wt.% and 75 wt. %, or between 35 wt. % and 65 wt. %, for example.

Stated otherwise, the first and second caprolactam-derived solvents maybe provided in various ratios, for example 1:1, 2:1, or 1:2.

More specifically, the caprolactam-derived solvent may include n-methylcaprolactam (N-MeCPL or NM CPL) present in an amount as little as 15 wt.%, 20 wt. %, or 25 wt. %, or as great as 65 wt. %, 75 wt. %, or 85 wt.%, based on the total weight of n-methyl caprolactam and n-ethylcaprolactam, or present in an amount within any range defined betweenany two of the foregoing values, and n-ethyl caprolactam (N-EtCPL or NECPL) present in an amount as little as 15 wt. %, 20 wt. %, or 25 wt. %,or as great as 65 wt. %, 75 wt. %, or 85 wt. %, based on the totalweight of n-methyl caprolactam and n-ethyl caprolactam, or present in anamount within any range defined between any two of the foregoing values.

Stated otherwise, n-methyl caprolactam and n-ethyl caprolactam may beprovided in various ratios, for example 17:3, 3:1, 2:1, 1:1, 1:2, 1:3,or 3:17, or any ratio therebetween.

II. Formation of PUDs

A. Traditional PUD Manufacturing Process—Solvent Acting as BothProcessing Solvent and Coalescing Agent.

With reference to FIG. 1 , in the traditional PUD manufacturing process100, a pre-polymer 110 is made through a reaction between a polymericdiol 102, and a poly- or di-isocyanate 104 in the presence of one ormore of the solvents 108 discussed above in Part I and a chain extender125. The pre-polymer or PUD resin 110 is generally of the formula:

The reaction between the polymeric diol 102 and the poly- ordi-isocyanate 104 further includes a hydrophilic agent 106 to introducethe carboxylic acid group. For example, the polymeric diol of thepre-polymer may be a hydroxyl-terminated polyether polyol, a polyesterpolyol, alkyds, polycarbonate polyol, polyamide polyol, or an acrylicpolyol, the poly- or di-isocyanate may be one of an aliphaticdiisocyanate or an aromatic diisocyanate or a polyisocyanate made of analiphatic or an aromatic diisocyanate such as tris(hexamethylenediisocyanate) trimer or isophorone diisocyanate trimer, for example, andthe hydrophilic agent may be either DMPA or polyethylene polyol-DMPA.Suitable chain extenders include dioal, alkylamine alcohols, andmixtures of amines and alcohols.

The chain-extended polyurethane pre-polymer or PUD resin 110 issubsequently mixed with at least one base or acid neutralizing agent 112and dispersed in water 114 to create a polyurethane dispersion 116. Thebase or the neutralizing agent is provided to allow the pre-polymer 110to be a water-soluble amine salt in the water 114. The base orneutralizing agent 114 is generally an amine such as trimethylamine, forexample.

In this traditional manufacturing process, the caprolactam-derivedsolvent acts as both the processing solvent and the coalescing agent forthe polyurethane dispersion, and the caprolactam-derived solvent may bepresent in an amount as little as 1 wt. %, 2 wt. %, or 3 wt. %, or asmuch as 6 wt. %, 8 wt. %, or 10 wt. %, based on the total weight of thepolyurethane dispersion, or may be present in an amount within any rangedefined between any two of the foregoing values, such as 1 wt. % to 10wt. % or 3 wt. % to 6 wt. %, for example.

B. Solvent-Free PUD Manufacturing Process—Solvent Acting as CoalescingAgent.

With reference to FIG. 2 , in the solvent-free PUD manufacturing process200, a pre-polymer or PUD resin 210 is made through a reaction between apolymeric diol 202, and a poly or di-isocyanate 204 in the presence of aprocessing solvent 208, typically acetone and/or methyl ethyl ketone(MEK), and a chain extender 225. The pre-polymer or PUD resin 210 isgenerally of the formula:

similar to pre-polymer/PUD resin 110. The reaction between the polymericdiol 202 and the diisocyanate 204 may further include a hydrophilicagent 206 to facilitate the reaction. The polymeric diol 202 of thepre-polymer/PUD resin 210 may be one of a polyether polyol, a polyesterpolyol, a polycarbonate polyol, a polyamide polyol, and an acrylicpolyol, the diisocyanate 204 may be one of an aliphatic diisocyanate oran aromatic diisocyanate, and the hydrophilic agent 206 may be dimethylbutanoic acid (DMBA). The polyurethane pre-polymer 210 may then be mixedwith at least one base 212, such as anamine, and dispersed in water 214to create a solution 218 of the polyurethane dispersion 216 and thesolvent 208.

The processing solvent 208 may be subsequently removed from the solutionof the polyurethane dispersion 216 and the solvent 208 to create thesolvent-free PUD 216. In particular, the solvent 208 may be removed fromthe solution via distillation or other similar methods.

However, in order for the solvent-free PUD 216 to exhibit good filmformation, and to enhance film hardness, open time, drying time andother properties desired from water-borne polyurethane dispersions, acoalescing agent, namely one or more of the caprolactam-derived solventsdiscussed in Part I above, may be used to lower the minimum film formingtemperature (MFFT). It may also be desired to use low volatile organiccompound (VOC) coalescing agents in waterborne coatings. Thecaprolactam-derived solvents discussed above in Part I are low VOCcoalescing agents and are suitable substitutes for volatile glycols,glycol ethers and alcohol esters in water-borne dispersions andemulsions.

C. PUDs with Blocked Isocyanates.

With reference to FIGS. 3 a, 3 b, 4 a and 4 b , either of the twomanufacturing processes discussed above may be slightly altered to formPUDs that include at least one blocked isocyanate group. In general,approximately 60% to 90% equivalent mol % of the isocyanate groups(i.e., N═C═O groups (NCO)) of the polyisocyanate or diisocyanate aretypically blocked on a given blocked PUD 326/426/526/626. As describedbelow, the manufacturing processes discussed above may be altered in oneof two ways such that the PUD formed includes at least one blockedisocyanate groups.

For example, referring to FIGS. 3 a and 3 b , the traditional andsolvent-free manufacturing processes may be altered by including ablocking agent 320/420 after forming a pre-polymer 321 to form apartially blocked polyurethane pre-polymer 322/422 where at least oneisocyanate group is blocked.

The partially blocked polyurethane pre-polymer 322/422 is generally ofthe formula:

where BA signifies isocyanate groups that are blocked with the blockingagent. As can be seen in the formula above, some isocyanate groupsremain unblocked, which are shown as the N═C═O groups in the aboveformula. In various embodiments, the partially blocked polyurethanepre-polymer 322/422 may be reacted with a chain-extender 325/425, suchas a diamine or triamine, to form a partially blocked and chain-extendedprepolymer of the formula:

The blocked PUD 326/426 formed from partially blocked polyurethanepre-polymer 322/422 through either process may then be applied as acoating or film on a substrate similar to the unblocked PUD.

With continued reference to FIGS. 3 a and 3 b , a blocked PUD 326/426may be formed from the partially blocked polyurethane pre-polymer322/422 using the traditional PUD manufacturing process 300 similar tothat discussed above in Part II(A) (FIG. 3 a ) or using the solvent-freePUD manufacturing process 400 similar to that discussed above in PartII(B) (FIG. 3 b ).

Referring to FIG. 3 a and using the traditional PUD manufacturingprocess 300, a polyisocyanate 304 may be reacted with polymeric diol 302and hydrophilic agent 306 in the presence of one or more of the solvents108 discussed above in Part I to create the pre-polymer 321. Thepre-polymer 321 may then be reacted with the blocking agent 320 to forma partially blocked pre-polymer 322, which may then be reacted with achain extender 325 to form PUD resin 310. The PUD resin 310 may besubsequently mixed with at least one base or acid neutralizing agent 312and dispersed in water 314 to create the blocked polyurethane dispersion(PUD) 326.

With reference to FIG. 3 b and using the solvent-free PUD manufacturingprocess 400, a polyisocyanate 404 may be reacted with polymeric diol 402and hydrophilic agent 406 in the presence of one or more of processingsolvents 408 to create the pre-polymer 421. The pre-polymer 421 may thenbe reacted with the blocking agent 420 to form a partially blockedpre-polymer 422, which may then be reacted with a chain extender 425 toform PUD resin 410. The PUD resin 410 may be subsequently mixed with atleast one base or acid neutralizing agent 412 and dispersed in water 414to create a solution 428 including the blocked polyurethane dispersion(PUD) 426 and the processing solvent 408. The processing solvent 408 maybe subsequently removed from the solution 428 of the blockedpolyurethane dispersion 426 and the solvent 408 to create thesolvent-free BPUD 426. For example, the solvent 408 may be removed fromthe solution 428 via distillation or other similar methods.

However, in order for the solvent-free BPUD 426 to exhibit good filmformation, and to enhance film hardness, open time, drying time andother properties desired from water-borne polyurethane dispersions, acoalescing agent, namely one or more of the caprolactam-derived solventsdiscussed in Part I above, may be used to lower the minimum film formingtemperature (MFFT) of the BPUD 426.

In various embodiments, one exemplary method of preparation of partiallyblocked PUDs using a partially blocked pre-polymer includes the stepsof:

-   -   1. Reacting a polyisocyanate component in a caprolactam-derived        solvent at 10-50 wt. % of the total composition mass with:        -   a. 50 to 90 equivalent mol %, of the NCO groups being            reacted with blocking agents that are capable of being            de-blocked thermally;        -   b. 0 to 25 equivalent mol % of the NCO groups being reacted            with polymeric diols having a polyether, polyester,            polyamide, polycarbonate, polyacrylic or alkyd backbone;        -   c. 10 to 15 equivalent mol %, of the NCO groups being            reacted with hydrophilic agents having hydroxyl and            carboxylic groups; and        -   d. 0 to 15% equivalent mol %, of the NCO groups being            reacted with a chain-extender that is at least difunctional            relative to NCO groups of the polyisocyanates;    -   2. Neutralizing the carboxylic groups of the above described        polyurethane dispersion polymer which has no free NCO groups        with a neutralizing agent; and    -   3. Dispersing the resulting polyurethane polymer in water or,        optionally, a dispersing aid such as dimethylethanol amine can        be used.

Another method includes altering the traditional and solvent-freemanufacturing processes to include the use of a partially blockedpolyisocyanate 524/624 formed by reacting a polyisocyanate 504/604 witha blocking agent 520/620. With reference to FIGS. 4 a and 4 b , ablocked PUD 526/626 may be formed from the partially blockedpolyisocyanate 524/624 using the traditional PUD manufacturing process500 similar to that discussed above in Part II(A) (FIG. 4 a ) or usingthe solvent-free PUD manufacturing process 600 similar to that discussedabove in Part II(B) (FIG. 4 b ).

Referring to FIG. 4 a and using the traditional PUD manufacturingprocess 500, the blocked isocyanate 524 may be reacted with polymericdiol 502 and hydrophilic agent 506 in the presence of one or more of thesolvents 108 discussed above in Part I and a chain extender 525 tocreate the PUD resin 510. The PUD resin 510 may be subsequently mixedwith at least one base or acid neutralizing agent 512 and dispersed inwater 514 to create the blocked polyurethane dispersion (PUD) 526.

With reference to FIG. 4 b and using the solvent-free PUD manufacturingprocess 600, the blocked isocyanate 624 may be reacted with polymericdiol 602 and hydrophilic agent 606 in the presence of at least oneprocessing solvent 608 and a chain extender 625 to create the PUD resin610. The PUD resin 610 may be subsequently mixed with at least one baseor acid neutralizing agent 612 and dispersed in water 614 to create asolution 628 of a blocked polyurethane dispersion (BPUD) 626 plus thesolvent 608.

The processing solvent 608 may be subsequently removed from the solution628 of the blocked polyurethane dispersion 626 and the solvent 608 tocreate the solvent-free BPUD 626. For example, the solvent 608 may beremoved from the solution via distillation or other similar methods.

However, in order for the solvent-free BPUD 626 to exhibit good filmformation, and to enhance film hardness, open time, drying time andother properties desired from water-borne polyurethane dispersions, acoalescing agent, namely one or more of the caprolactam-derived solventsdiscussed in Part I above, may be used to lower the minimum film formingtemperature (MFFT) of the BPUD 626.

In various embodiments, one exemplary method for the preparation ofblocked solvent-free PUDs using a blocked isocyanate includes the stepsof:

-   -   1. Reacting a polyisocyanate component (e.g. Trimers of HDI,        IPDI) in caprolactam-derived solvent at 10-50 wt. % of the total        mass with:        -   a. 10 to 25 equivalent mol %, based on the NCO groups is            reacted with hydrophilic agents having hydroxyl and            carboxylic groups;        -   b. 10 to 15 equivalent mol % based on the NCO groups is            reacted with polymeric diols having polyether, polyester,            polyamide, polycarbonate, polyacrylic, alkyd, castor oil or            linseed oil backbone; and        -   c. 60 to 80 equivalent mol %, based on the NCO groups is            reacted with blocking agents that are capable of being            de-blocked thermally.

Once applied, the blocked PUD undergoes a two-step cure instead of theone-step cure of the unblocked PUD. The first step of the two-step cureincludes a dry cure in which the PUD partially cures on the surface ofthe substrate, wherein the water evaporates to leave the coating orfilm, and particles of the PUD coalesce to form a thick sticky layer orfilm. Since the dry cure typically occurs at room or ambienttemperature, the blocked isocyanate groups remain blocked and unable toreact with surrounding reactants. Subsequently, the second step of thecure includes a heat cure in which the PUD coating is heated at anelevated temperature as little as 80° C., 90° C., or 100° C., or as highas 130° C., 140° C., or 150° C., or within any range defined between anytwo of the foregoing values, such as 80° C. to 150° C., 90° C. to 140°C., or 100° C. to 130° C., for example, in which the de-blockedisocyanate groups undergo crosslinking.

Once the blocked PUD is heated, the blocked isocyanate groups liberatethe blocking agent creating an unblocked PUD, allowing the unblockedisocyanate groups to react with moisture in the air or other componentsof the PUD, and the blocking agent and/or coalescing agent to leave thefilm. An example reaction of the heat cure is as follows:

where BL is the blocking agent, R is the remainder of the PUD, and R′can be hydrogen, an acid, or and amine, for example.

Blocking agents suitable for use in the process according to theinvention are, in particular, compounds with preferably oneisocyanate-reactive group which enter into an addition reaction withorganic isocyanates at temperatures above about 50° C. and preferably attemperatures in the range of from about 80° to 180° C., and whoseresulting addition products, in admixture with involatile polyolscontaining primary hydroxyl groups, react with the involatile polyols toform urethanes at temperatures in the range of from about 100° to 200°C., the reaction being accompanied by liberation of the blocking agent.Suitable blocking agents of this type are, for example, alcoholsincluding secondary or tertiary alcohols, such as isopropanol ortert-butanol, phenols such as phenol and nonylphenol, C—H-acidcompounds, including compounds having active methylene groups, such asmalonic acid diesters including dimethylmalonate, diethylmalonate,oximes, such as formaldoxime, acetaldoxime, acetone oxime, methyl ethylketoxime, methyl propyl ketoxime, methyl isopropyl ketoxime,cyclohexanone oxime, acetophenone oxime, 2-pentanone oxime, benzophenoneoxime, butanone oxime, or diethyl glyoxime, pyrazole class of compoundssuch as 1,2-pyrazole, 3,5-dimethylpyrazole, 1,2,4-triazole, imidazoleclass of compounds such as ethyl imidazole, cylicamides includinglactams such as caprolactam, ester amines such as alkylalanine esters,and other various blocking agents such as acetyl acetone, acetoaceticacid alkyl esters, benzyl-tert-butylamine, diispropylamine,isopropylamine, ethyl acetoactetate and/or mixtures thereof.

IV. Properties

a. Viscosity

Viscosity is the extent to which a fluid resists a tendency to flow. Theviscosity of a paint or coating will affect the ease of brushing,coverage, and tendency to spatter. Typically, a paint or coating isdesired to have a viscosity in which it brushes with sufficient ease,properly covers the substrate it is applied to without brush marks, andhas a small tendency to spatter. Viscosity may be determined inaccordance with ASTM D4179-11. In general, the viscosity of a paint orcoating of the present disclosure may be as low as 0.05 Pa·s, 0.08 Pa·s,0.2 Pa·s, 0.5 Pa·s or 1.0 Pa·s, as high as 1 Pa·s, 1.5 Pa·s, 2 Pa·s, or4 Pa·s, or within any range defined between any two of the foregoingvalues, such as 0.05-4 Pa·s, 0.05-2 Pa·s, 0.5-1.5 Pa·s, or 0.05-1 Pa·s,for example.

b. Storage Stability

Storage stability of a coating or paint correlates with its low shearviscosity (LSV). Thus, storage stability can be tested by viscositymeasurements and microscopy before and after heat aging. In general,lower or more constant viscosities indicate good storage stability for apaint or coating. More specifically, lower or more constant viscositiesindicate that the paint or coating would be useful for a longer periodof time. For instance, PUDs of the present disclosure may have a storagestability of at least 6 weeks at 40° C. or alternatively may remainstable for 6 to 12 months.

Storage stability may be determined by evaluating viscosity measurementsshortly after the PUD is prepared and after storage for either one monthat room temperature or one month at 50° C.

c. Minimum Film Forming Temperature

The minimum film-forming temperature (MFFT) of a paint or coating is thelowest temperature at which the paint or coating will uniformly coalescewhen applied to a substrate as a thin film. Thus, for effective use, itis important that paints and coatings be applied only to surfaces with atemperature above that of their MFFT. Accordingly, the lower the MFFT ofa paint or coating, the more durability the paint or coating willexhibit over a wider variety of temperatures. Minimum film-formingtemperatures may be determined in accordance with ASTM D 2354 and ISO2115. In general, MFFT of a paint or coating of the present disclosuremay be as low as −2.5° C., −2.0° C., −1.5° C., as high as −1.0° C.,−0.5° C., or 0° C., or within any range defined between any two of theforegoing values, such as −2.5° C. to 0° C., −1.4° C. to 0° C., or −1.7°C. to −0.4° C., for example.

d. Film Formation

Film formation of a coating or paint is characterized by the efficiencyof the coalescing agent to plasticize temporally the polymeric particlesresulting in a continuous film formation. In general, a paint or coatingwith good film formation will show little to no cracking when applied insevere conditions. A paint or coating with good film formation isimportant for providing a constant film or coating that is notdefective.

e. Open Time

The open time of a paint or coating is the length of time a paintremains “wet” or “open” enough to allow for brush-in and repair. Opentime is a key performance property for coatings, particularly for brushapplications.

Open time may be determined in accordance with ASTM D7488. In general,open time for a paint or coating of the present disclosure may be as lowas 5, 10, or 15 minutes, as high as 20, 22, or 25 minutes, or within anyrange defined between any two of the foregoing values, such as 5-25minutes, 10-22 minutes, or 14-22 minutes, for example. Advantageously,the longer the open time, the longer the paint or coating can be fixedbefore it dries. As such, if the paint of coating is scratched or marredafter applied, the paint or coating can be modified for uniformthickness, etc., by the user before the paint or coating begins drying.In addition, longer open times can reduce overlapping coating defectswhen the paints or coatings are applied over large areas. Longer opentimes are also useful for decorative techniques, such as feathering orglazing. Further benefits of longer open times also include reducedlabor and material costs in requiring less time and supplies to fixdefects. Longer open time can also be important for small scale jobssuch as crafts, trim painting and finger nail polish as well.

f. Drying Time

The drying time of a paint or coating is the length of time it takes thepaint or coating to reach a stage where the applied paint or coating canjust be touched, or sand impinging on the surface of the drying coating,can be brushed off, without damaging the surface of the coating. Thedrying times of a paint or coating are significant in determining when afreshly painted or coated room, floor, or stair, for example, may be putback in use or a coated article may be handled or packaged. In general,paints or coatings have many different surface drying times but ingeneral they all fall roughly into one of the following categories:ultra quick dry (0-5 minutes), quick dry (5-20 minutes), 0.5 to 1 hour,1.5-3 hours, or 4-8 hours. Advantageously, the shorter the dry time, thequicker the paint or coating is dry and the sooner the room or articlemay be used or recoated.

Drying time may be determined in accordance with ASTM D1640 or ASTMD5895. In general, the drying time for a paint or coating of the presentdisclosure may be as low as 10 minutes, 12 minutes, or 14 minutes, ashigh as 16 minutes, 18 minutes, or 20 minutes, or within any rangedefined between any two of the foregoing values, such as 10-20 minutes,12-20 minutes, or 14-20 minutes, for example.

g. Persoz Hardness

Hardness is related to the dampening properties of an organic surface.Specifically, hardness is the resistance of a coating or paint to amechanical force. A lower stiffness or resistance will result in deeperindentation of a ball of a testing apparatus into the material resultingin a faster dampening of the oscillations and finally, a lower hardness.Advantageously, a higher hardness indicates a stronger or more durablepaint or coating. A coating or paint having a Persoz hardness ofapproximately 110 to approximately 135 is considered good.

Persoz hardness may be determined in accordance with ISO 522. Ingeneral, the hardness at 28 days for a paint or coating of the presentdisclosure may be as low as 100 seconds, 110 seconds, or 115 seconds, ashigh as 120 seconds, 125 seconds, or 130 seconds, or within any rangedefined between any two of the foregoing values, such as 100-130seconds, 104-130 seconds, or 104-127 seconds, for example.

h. Gloss and Color

Gloss is the smoothness of the coating or paint and/or substrate on amicroscopic level. When the coating or paint and/or substrate are bothvery smooth, light will reflect in a uniform direction creating a highgloss finish. On the other hand, when the coating or paint and/orsubstrate are both rough on a microscopic level, light will scatter inmultiple directions creating a lower gloss or a flat finish. Whenmeasuring gloss, a value can be given to a finish by looking at thefinish at different angles. In general, 100 is typically the highestvalue for gloss and zero is the lowest.

High gloss finishes typically have a value of 70 through 100 and need tobe measured with a 20° gloss meter, glosses ranging from 10 and 70should be measured with a 60° gloss meter, and flat finishes from 0through 10 should be measured with an 85° gloss meter.

Gloss may be determined in accordance with ISO 2813 and USO 7724-2. Ingeneral, the gloss of the paints and/or coatings of the presentdisclosure may be as low as 1.0-1.5 when measured with a 20° glossmeter, 2.5-3.5 when measured with a 60° gloss meter, and 15-35 whenmeasured with an 85° gloss meter, or within any of range defined betweenany two of the foregoing values.

i. Scrub Resistance

Scrub resistance is the ability of the paint or coating to resistwearing or degradation once the paint or coating has dried to form afilm. The wear or degradation is assessed either visually or by weightor thickness loss. The importance of evaluating the scrub resistance ofa paint is to confirm that it will maintain the expected visualappearance after washing with a brush or cloth to remove dirt and othermarkings, and that it will maintain its physical properties, i.e., nosoftening, blistering, or thinning, when exposed to cleaning products.If the paint or coating shows any visual changes in appearance whencompared to a non-scrubbed area, then the paint is said to possess poorscrub resistance.

Scrub resistance may be determined in accordance with ISO 11998. Ingeneral, the weight loss of the paints and/or coatings of the presentdisclosure may be as low as 2.0 g/m² or 2.5 g/m², as high as 4.0 g/m² or4.5 g/m², or within any range defined between any two of the foregoingvalues, such as 2.0-4.5 g/m² or 2.4-4.4 g/m², for example, and the lossof thickness of the paints and/or coatings of the present disclose maybe as low as 1.0 μm or 1.5 μm, as high as 2.5 μm or 3.0 μm, or withinany range defined between any two of the foregoing values, such as1.0-3.0 μm or 1.5-3.0 μm, for example.

j. Freeze/Thaw Stability

Freeze/thaw stability characterizes the ability of a paint or coating towithstand changes in temperature that can often be substantial. Ingeneral, a paint or coating with good freeze/thaw stability has theability to be cycled through various changes in temperature and still beuseful as a paint or coating. A good freeze/thaw stability isadvantageous as it allows the user to store a paint in any temperatureand the paint or coating will remain useful even if the temperature ofthe paint or coating has changed drastically, thus resulting in a longerlasting paint or coating. Freeze/thaw stability may be determined inaccordance with ASTM D2243-95.

As used herein, the phrase “within any range defined between any two ofthe foregoing values” literally means that any range may be selectedfrom any two of the values listed prior to such phrase regardless ofwhether the values are in the lower part of the listing or in the higherpart of the listing. For example, a pair of values may be selected fromtwo lower values, two higher values, or a lower value and a highervalue.

EXAMPLES Example 1—Solubility of Solvents

Solubility was tested between the various solvents to determine theirapplicability in the PUD manufacturing processes. Solubility is theamount of a substance (coalescing agent) that dissolves in a unit volumeof a liquid substance (solvent) to form a saturated solution underspecified conditions of temperature and pressure. For the examples,amounts of depomedroxyprogesterone acetate (DMPA) were dissolved in eachsolvent. As seen in Table 1 below, dimethylformamide (DMF) provided thebest solubility at 63.9 grams of DMPA in 100 grams of solvent, followedby NMP (54.0 grams of DMPA), n-methyl caprolactam (N-MeCPL) (27.5 gramsof DMPA), a mixture of N-MeCPL and n-ethyl caprolactam (N-EtCPL) in aratio of 2:1 (25.0 grams of DMPA), a mixture of N-MeCPL and N-EtCPL in aratio of 1:1 (22.5 grams of DMPA), a mixture of N-MeCPL and N-EtCPL in aratio of 1:2 (20.0 grams of DMPA), N-EtCPL (20.0 grams of DMPA),3-n-butylphthalide (NBP) (20.0 grams of DMPA), esteramine (10.0 grams ofDMPA), n-butyl caprolactam (N-BuCPL) (10.0 grams of DMPA), andesteramide (10.0 grams of DMPA). While the caprolactam-derived solvents(N-MeCPL, N-EtCPL, N-BuCPL) do not have as high of a solubility of NMPand DMF, the solubility of N-MeCPL, and the mixtures of N-MeCPL andN-EtCPL in ratios of 2:1 and 1:1 is sufficient to adequately dissolveDMPA for the manufacturing of PUDs.

TABLE 1 Solubility of DMPA in Solvents Solubility Solvents (g/100 g ofSolvent) DMF 63.9 NMP 54.0 N—MeCPL 27.5 N—MeCPL/N—EtCPL - 2:1 25.0N—MeCPL/N—EtCPL - 1:1 22.5 N—MeCPL/N—EtCPL - 1:2 20.0 N—EtCPL 20.0 NBP20.0 Esteramine 10.0 N—BuCPL 10.0 Esteramide 10.0

Example 2—Compatibility of Coalescing Agents with PUD Resins

Coalescing agents were also tested for their compatibility with purepolyurethane dispersion resins and for visual observation of the filmfor transparency, homogeneity, and phase separation. In order toproperly test these properties, pigments and other opacifying materialswere not added to the formulations. The samples were made by mixing asolvent-free polyurethane dispersion, Alberdingk® PUR-MATT 970 VP,having 34-36% solids with 5 wt. % (based on the polyurethane resin) ofthe coalescing agent.

a. Visual Observation of PUD Film

The transparency, homogeneity, and phase separation of each film wasobserved once each of the films has dried. With reference to Table 2below, visual observation of the films showed that caprolactam-derivedsolvents, N-methyl and N-ethyl, exhibited good film properties, i.e.,good transparency and homogeneity.

TABLE 2 Visual Evaluation of Dry Film Visual Evaluation Composition ofDry Film Resin* only micro cracks Resin + Ester alcohol bubbles & cracksResin + N-butyl pyrrolidone (NBP) Pass Resin + Ester amide^(a) PassResin + N-methyl CPL Pass Resin + N-ethyl CPL Pass Resin + N-butyl CPLagglomerates *PU Alberdingk PURMatt 970VP ^(a)Hexanoic acid,6-(dimethylamino)-6-oxo, methyl ester

b. Minimum Film Forming Temperature of Coalescing Agents

Minimum film forming temperatures, MFFT, were measured using a MFFTtemperature bar (MFFT-BAR) according to the standard test methods ASTM2354 and ISO 2115, with the film having a thickness of 350 μm. Withreference to Table 3 below, the MFFTs of the caprolactam-derivedcoalescing agents, N-methyl caprolactam (N-methyl CPL), N-ethylcaprolactam (N-ethyl CPL), N-butyl caprolactam (N-butyl CPL), esteralcohol, and ester amide, had similar or better MFFTs (−0.8±0.4,−1.4±0.3, and −1.3±0.3, respectively) than NBP (−0.4±0.2).

TABLE 3 MFFTs of Coalescing Agents Composition MFFT (° C.) Resin* only30 Resin + Ester alcohol 0 Resin + N-butyl pyrrolidone (NBP) −0.4 ± 0.2Resin + Ester amide^(a) −0.7 ± 0.2 Resin + N-methyl CPL −0.8 ± 0.4Resin + N-ethyl CPL −1.4 ± 0.3 Resin + N-butyl CPL −1.3 ± 0.3 *PUAlberdingk PURMatt 970VP ^(a)Hexanoic acid, 6-(dimethylamino)-6-oxo,methyl ester

c. Persoz Hardness of Coalescing Agents

Persoz hardness of each coalescing agent was measured according to theISO 1552 standard test method. With reference to Table 4 below, thecaprolactam-derived coalescing agents, N-methyl and N-ethyl, showedsimilar or higher Persoz hardness after 28 days in comparison to NBP andester alcohol.

TABLE 4 Compatibility of Non-Pigmented PUDs with Pure PolyurethaneDispersion Resins Persoz Hardness (sec) 2 7 14 21 28 Composition Resin*only Days Days Days Days Days Resin + Ester alcohol 75 97.6 107.4 113.4116.8 Resin + N-butyl pyrrolidone 70 103.2 110.4 115.4 117.8 (NBP)Resin + Ester amide^(a) 61 74.0 78.0 80.0 83.0 Resin + N-methyl CPL 72103.0 113.2 116.8 117.8 Resin + N-ethyl CPL 73 102.0 112.0 118.0 118.0Resin + N-butyl CPL 68 89.0 101.0 110.0 113.0 *PU Alberdingk PURMatt970VP ^(a)Hexanoic acid, 6-(dimethylamino)-6-oxo, methyl ester

VI. Example 3—Coalescing Properties of the Caprolactam-Derived Solvents

Various coalescing properties of caprolactam-derived solvents of thepresent disclosure were tested in comparison with other known coalescingagents such as 2, 2, 4-trimethyl-1,3-pentanediol monoisobutyrate,N-methyl pyrrolidone (NMP) and N-butyl pyrrolidone (NBP).

Tests were first performed to determine the coalescing agent level forpigmented and complete PUD formulations in order to achieve the optimumfilm formation. Complete paints were mixed with 0.7 wt. %, 1.5 wt. %,3.0 wt. % and 5.0 wt. % of coalescing agents and applied on tin platedsteel at a wet film thickness of around 250 μm, where the weightpercentage was based on the pure polyurethane dispersion resins. The dryfilms were observed for cracking and surface defects using an opticalmicroscope. Based on the observations, 3 wt. % dosage of coalescingagent was selected. Complete PUD formulations with pigments, fillers andother additives were prepared as per Table 5, and used to test anddetermine the coalescing properties of the caprolactam-derived solventsand other known coalescing agents.

TABLE 5 PUD-Pigmented Formulations Content Source Weight (parts) Water14.25 Dispersant Orotan ™ 731 1.3 Antiform Tego ® foamex 810 0.1Rheology modifier Aquaflow ™ NLS-205 0.4 Pigment Kronos ® 2190 18.4Calcium carbonate Hydrocarb OG 4.5 Fillers Sillitin Z 89 2.7 AntifoamTego ® airex 902 W 0.1 Total 41.75 Water 10.4 Resin Alberdingk ® PURMATT 970 40 VP Rheology modifier Aquaflow ™ NLS-205 1.8 Coalescing Agent3.0 Total 55.2 TOTAL 96.95

Coalescing properties of caprolactam-derived solvents of the presentdisclosure were determined to be generally comparable or better than theother known coalescing agents.

a) Viscosity and Storage Stability

Dispersions and emulsions tend to aggregate polyurethane particlesduring storage. One way to determine the stability of a polyurethanedispersion is to measure viscosity of the polyurethane dispersion overtime. Viscosity is a measure of a solvent's resistance to gradualdeformation by shear stress or tensile stress. Exemplary formulationswere tested for viscosities using a compression testing device todetermine crush resistance in accordance with the ASTM D4179-11standard, and titration techniques to determine degrees of termination.The storage stability of the dispersions was evaluated based onvariations between viscosity measurements performed on paints shortlyafter their preparation and after their storage for either one month atroom temperature or one month at 50° C. In general, the lower theviscosity of a solvent, the more stable the solvent, and thus the betterthe solvent.

With reference to FIG. 5 , the storage stability of pigmented PUDformulations using caprolactam-derived solvents, N-ethyl CPL andN-methyl CPL, showed overall better performance (low viscosity buildup)for the accelerated condition of 1 month at 50° C. as compared to NBPand similar performance as compared to NMP.

b) MFFT and Film Formation in Severe Conditions

The standard test for determining this temperature involves using aMFFT-BAR, as specified by standards ASTM D 2354 and ISO 2115. Ingeneral, the MFFT of a paint or coating is reduced temporarily by theuse of coalescing agents.

Caprolactam-derived solvents of the present disclosure showed good MFFTin pigmented polyurethane dispersions. For instance, as seen below inTable 4, N-ethyl CPL had a lower temperature than NMP, and N-methyl CPLhad a substantially similar temperature to NBP.

The efficiency of the coalescing agents to form films in severeconditions (4° C.) was also tested by applying the paints on tin platedsteel at a humid thickness of 200 μm. As shown below in Table 6,N-methyl CPL, N-ethyl CPL, and N-butyl CPL all performed efficiently insevere conditions with no cracks detected, while NMP and ester alcoholhad micro cracks.

TABLE 6 Minimum Film Forming Temperature of Pigmented and Complete PUDsand Observations of Film Formation in Severe Conditions MFFT FilmFormation at Composition (° C.) 4° C.: Observation N-ethyl CPL (NE CPL)−2.4 OK (no cracks) N-methyl pyrrolidone (NMP) −1.4 micro cracksN-methyl CPL (NM CPL) −0.8 OK (no cracks) N-butyl pyrrolidone (NBP) −0.7OK (no cracks) Ester alcohol −0.4 micro cracks Ester amide^(a) −0.6general cracks 1:2 NE CPL:NM CPL — OK (no cracks) 1:1 NE CPL:NM CPL — OK(no cracks) 2:1 NE CPL:NM CPL — OK (no cracks) ^(a)=2,2,4-trimethyl-1,3-pentanediol monoisobutyrate

c) Open Time

Open times were determined according to the ASTM D7488 “Test Method forOpen Time of Latex” standard and the tests were performed undercontrolled temperature and humidity (23±2° C. and 50±5% RH). In general,the paints were applied at a wet film thickness of 200 μm on contrastingsealed charts by means of a doctor blade applicator, and “X” marks aremade immediately with the wide curved end of a wooden paint brush. Aftera determined time internal, the brush was dipped into the paint to betested and brushing of the X-marks was started in perpendiculardirection to the initial drawdown using 10 strokes back and forth towork the paint under test into the drawdown area. This procedure isrepeated after several time intervals. After their complete drying (1week), the painted panels are observed by two different observers andthe time for which the “X” marks to become visible is considered as theopen time.

With reference to FIG. 6 and Table 7 below, caprolactam-derivedsolvents, N-ethyl CPL and N-methyl CPL, had longer open times, 16minutes and 14 minutes, respectively, than other coalescing agents, suchas NMP, 12 minutes, and NBP, 12 minutes, and ester amide had a similaropen time to NMP and NBP, specifically, 12 minutes. However, blends ofcaprolactam-derived solvents, 1:1 N-ethyl CPL:N-methyl CPL, 1:2 N-ethylCPL:N-methyl CPL, and 2:1 N-ethyl CPL:N-methyl CPL, had even longer opentimes, 20 minutes, 22 minutes, and 18 minutes, respectively, than bothcaprolactam-derived solvents alone or other coalescing agents.Advantageously, blends of caprolactam-derived solvents, 1:1 N-ethylCPL:N-methyl CPL, 1:2 N-ethyl CPL:N-methyl CPL, and 2:1 N-ethylCPL:N-methyl CPL also had open times, 20 minutes, 22 minutes, and 18minutes, respectively, that were longer than their drying times, 17.7mins, 15.9 mins, and 16.4 mins, respectively.

d) Drying Time

The drying times for the pigmented PUD formulations were determinedaccording to the ASTM D1640 “Standard Test Methods for Drying, Curing,or Film Formation of Organic Coatings” standard or the ASTM D5895“Standard Test Methods for Evaluating Drying or Curing During FilmFormation of Organic Coatings Using Mechanical Recorders” standard. Fourstages of drying can be identified depending on the trace left by theneedle on the paint surface: Stage 1—Set-to-Touch time, Stage2—Tack-Free time, Stage 3—Dry-Hard time, and Stage IV—Dry trough time.However, Stage IV is often hard to detect.

In general, the paints were applied at a humid film thickness of 200 μmby means of a bar coater on a Leneta sheet and the needle rate was setat 60 cm/hr.

For the present examples, the drying times for the 2:1 A:B, 1:1 A:B, and1:2 A:B solvents were determined using the ASTM D1640 standard, and thedrying times for NM CPL, NE CPL, NMP, NBP, ester amide, and esteralcohol were determined using the ASTM D5895 standard. With reference toFIG. 7 and Table 7 below, overall, caprolactam-derived solvents,N-methyl (NM CPL), N-ethyl (NE CPL), ester amide, and ester alcohol andthe blends (2:1, 1:1, 1:2) of NM CPL and NE CPL, had shorter dryingtimes (11.6 minutes, 17.4 minutes, 13.3 minutes, 13.6 minutes, 17.7mins, 15.9 mins, and 16.4 mins, respectively) as compared to NMP (19.8minutes), and NM CPL had a similar drying time (11.6 minutes) ascompared to NBP (11.8 minutes).

TABLE 7 Open and Drying Times Composition Drying Time (min) Open Time(min) NM CPL (A) 11.6 14 NE CPL (B) 17.4 16 2:1 A:B 17.7 20 1:1 A:B 15.922 1:2 A:B 16.4 18 NMP 19.8 12 NBP 11.8 12 Ester amide 13.3 12 Esteralcohol 13.6 10From the above Table, it may be observed that blends of the solventstypically have shorter drying times than open times, whereas thesolvents themselves and other solvents typically have longer dryingtimes than open times.

e) Persoz Hardness

Hardness is related to the dampening properties of organic surfaces. Alower stiffness will result in deeper indentation of the ball into thematerial resulting in a faster dampening of the oscillations andfinally, a lower hardness.

Persoz hardness measurements were performed on pigmented paints thatwere applied on tin plated steel using a doctor blade applicator at adry film thickness (DFT) around 50 μm according to the ISO 1522standard. With reference to Table 8 below, twenty-eight (28) dayhardness for the caprolactam-derived solvents was shown to be similar tothat of other coalescing agents. For instance, the 28 day hardness forN-ethyl caprolactam (NE CPL) was approximately 104.6±0.5, while the 28day hardness for NMP was approximately 108.8±2.4, and the 28 dayhardness for ester alcohol and N-methyl caprolactam (NM CPL) wereapproximately 124.8±1 and 126.0±1, respectively, while the 28 dayhardness for NBP was approximately 135.8±5. In addition, the hardness ofpaints or coatings with the blends of NM CPL and NE CPL were shown to bein a similar range, for example the blends of NM CPL and NE CP1 wereapproximately 110-120 seconds, while the hardness of NMP and NBP wereapproximately 105-140 seconds.

TABLE 8 Persoz Hardness of Pigmented and Complete PUDs ThicknessComposition (mm) 1 Day 7 Days 14 Days 21 Days 28 Days Ester alcohol 42.298.2 ± 3 118.0 ± 1   120.0 ± 2   122.0 ± 2   124.8 ± 1   NBP 45.2 64.4 ±3 127.0 ± 2   133.2 ± 5   136.6 ± 6   135.8 ± 5   NMCPL 46.8 95.2 ± 1101.2 ± 3   122.0 ± 3   124.0 ± 3   126.0 ± 1   NMP 54.7   94.2 ± 0.4101.0 ± 2.4 100.6 ± 1.7 107.6 ± 1.3 108.8 ± 2.4 NE CPL 52.2  101.0 ± 1.0102.0 ± 0.7 101.4 ± 2.6 104.0 ± 2.8 104.6 ± 0.5 1:1 NM 78.2   79.0 ± 1.0101.0 ± 1.0 102.4 ± 1.0 104.1 ± 1.0 111 ± 3 CPL:NE CPL 2:1 NM 90.8 94.2± 1 103.0 ± 1.0 106.1 ± 1.0 105.0 ± 1.2 116 ± 2 CPL:NE CPL 1:2 NM 80 80.0 ± 11 102.0 ± 1.0 105.0 ± 1.1 103.1 ± 1.1 115 ± 3 CPL:NE CPL

f) Gloss and Color

Gloss measurements serve as an indicator of the paints surface quality.Gloss and color measurements were determined according to the ISO 2813standard and the ISO 7724-2 standard (SCI-D65/10°), respectively.

With reference to Tables 9 and 10, the gloss and color measurements ofthe caprolactam-derived solvents, n-methyl (NM CPL), n-ethyl (NE CPL),and their blends, showed an increase in gloss and did not affect thecolor (i.e., no yellowing).

TABLE 9 Gloss of Pigmented and Complete PUDs Composition 20° 60° 85°Ester alcohol 1.3 ± 0 3.0 ± 0 19.6 ± 0.3 Ester amide 1.3 ± 0 3.3 ± 024.2 ± 0.2 NBP 1.3 ± 0 2.8 ± 0 19.9 ± 0.2 NMP 1.3 ± 0 3.6 ± 0 30.7 ± 0.6NM CPL 1.3 ± 0 3.0 ± 0 23.2 ± 0.2 NE CPL 1.3 ± 0 3.0 ± 0 24.5 ± 0.5 1:1NM CPL:NE CPL 1.3 ± 0 3.0 ± 0 23.3 2:1 NM CPL:NE CPL 1.3 ± 0 3.1 ± 024.2 1:2 NM CPL:NE CPL 1.3 ± 0 3.1 ± 0 24.7

TABLE 10 Color of Pigmented and Complete PUDs Color (White background)Color (Black background) Composition L* a* b* L* a* b* Ester alcohol95.6 −0.51 3.16 94.93 −0.87 2.30 Ester amide 94.98 −0.51 3.29 93.84−1.05 2.03 NBP 95.01 −0.56 3.32 94.00 −1.04 2.20 NMP 95.14 −0.52 3.0294.55 −0.88 2.20 NMCPL 95.07 −0.52 3.32 94.09 −0.97 2.25 NE CPL 95.04−0.61 3.24 94.45 −0.92 2.46 1:1 NM N/A N/A N/A 94.48 −0.95 2.22 CPL:NECPL 2:1 NM N/A N/A N/A 94.50 −0.94 2.37 CPL:NE CPL 1:2 NM N/A N/A N/A94.33 −1.03 2.28 CPL:NE CPL

g) Scrub Resistance

Scrub resistance was tested according the ISO 11998 “Paints andVarnishes—Determination of Wet-Scrub Resistance and Cleanability ofCoatings” standard. In this testing method, the paint was applied on atest panel (Leneta sheet) using a film applicator at the specific gapclearance. After drying and conditioning for four weeks at roomtemperature the coated panel was weighed and subject to 200 wet-scrubcycles in a scrub resistance machine. The panel was then washed, driedand weighed to determine the loss from which the mean loss in filmthickness was calculated. With reference to Table 11 below,caprolactam-derived coalescing agents showed better film formation andthe paints were more resistant to the brush action as compared to NMP.For instance, N-methyl caprolactam (NM CPL), N-ethyl caprolactam (NECPL), and blends thereof in the ratios of 1:2 and 1:1, all had less lossof thickness (2.035 μm, 1.797 μm, 1.39 μm, and 1.64 μm, respectively) ascompared to NMP (2.090 μm) and NBP (2.213 μm). In addition, blends ofcaprolactam-derived solvents NM CPL and NE CPL showed the least amountweight loss (2.409 g/m² (1:1) and 2.955 g/m² (1:2)) as compared to theother coalescing agents.

TABLE 11 Scrub Resistance of Pigmented and Complete PUDs Loss ofthickness Wt. Loss after 200 wet- Composition (g/m²) scrub cycles (□m)Ester alcohol 7.747 4.439 Ester amide 7.920 4.040 NBP 4.142 2.213 NM CPL3.763 2.035 NE CPL 3.767 1.797 NMP 3.372 2.090 1:1 NM CPL:NE CPL 2.4091.39 2:1 NM CPL:NE CPL 4.324 2.69 1:2 NM CPL:NE CPL 2.955 1.64

h) Freeze and Thaw Stability

Water-based emulsions and dispersions are susceptible to irreversiblecoagulation by freezing. Freeze and thaw stability was tested accordingthe ASTM D2243-95 standard.

For these examples, pigmented PUD paints were subject to freeze-thawcycles of 16 hours at −20° C. and 8 hours at room temperature andsubsequently subject to visible observations. The paints were thenapplied on a tin plated steel plate at a thickness of approximately 200μm for observing film properties.

With reference to FIGS. 8 and 9 , caprolactam-derived coalescing agents,N-methyl caprolactam (NM CPL) and N-ethyl caprolactam (NE CPL), and 1:1,1:2, and 2:1 blends thereof showed better freeze-thaw stability and filmproperties than NBP and ester alcohol, and showed similar freeze-thawstability as compared to NMP. In addition, the freeze-thaw stability wasbest for caprolactam-derived coalescing agents (NM CPL) and the blendseven after subject to five cycles (see FIG. 9 ). In particular, thepaints were visually observed after each cycle to see if there was anyviscosity change, i.e., thickening of the paint. Then, the dry films ofthe coatings were observed visually. As may be seen from FIGS. 8 and 9 ,n-butyl pyrrolidone and ester alcohol showed thickening of the paintsamples after two cycles, whereas N-methyl caprolactam showed no suchviscosity change even after five freeze-thaw cycle and showed good filmformation.

Example 5— Synthesis of Partially Blocked Polyurethane DispersionsExample 5a—Synthesis of Partially Blocked PolyurethaneDispersions—Blocked Polyisocyanate

A partially blocked polyurethane dispersion was synthesized using ablocked polyisocyanate by charging a reactor equipped with stirrer andcondenser with 1.01 molar equivalent of a polyisocyanate, (e.g. HDITrimer; Trade name: Desmodur N3300 from Covestro) in N-alkyl caprolactamor blends thereof, and heated to 50° C. under a nitrogen atmosphere.Subsequently, 0.7 molar equivalent of a blocking agent (e.g. 2-pentanoneoxime or 2-butanone oxime) was added dropwise over a period of time(approximately 1 hour) and left at 60-70° C. until a constant NCO valuewas reached. To this partially blocked polyisocyanate, 0.1 molarequivalent of a diol (1,6-heaxne diol or hydroxyl terminated polyol) and0.2 molar equivalent of dimethylol propionic acid (DMPA) were added andstirred at 80-90° C. until all the NCO groups were consumed (monitoredby IR spectroscopy). The reaction mixture was cooled to 80° C. and0.2-0.25 equivalent of a neutralizing agent (e.g.N,N-Dimethylethanolamine, or Triethyl amine) was added and the stirringcontinued for another 15-30 minutes. Deionized water (475-480 g/mol ofpolyisocyanate) was added with the content stirred at 50° C. foradditional 2 hours. The content was then cooled to room temperature. Thesolid content of the dispersion was 37-38%, at a pH about 9.0.

Example 5b—Synthesis of Partially Blocked PolyurethaneDispersions—Blocked Pre Polymer

A partially blocked polyurethane dispersion was synthesized using ablocked pre-polymer by charging into a reaction vessel equipped with astirrer and a reflux condenser 1.0 molar equivalent of Hydroxylterminated polyol (e.g. PTMG, M_(n)=1000 and 2000 gmol⁻¹), 1.0 molarequivalent of dimethylol propionic acid (DMPA) and 150 grams of N-alkylcaprolactam or blends thereof. While stirring at 70-75° C. under anitrogen atmosphere, 2.67 molar equivalent of diisocyanate (MDI) in 150grams of N-alkyl caprolactam or blends thereof was added to the reactionmixture. The change in isocyanate (NCO) content was monitored, using astandard titration (di-n-butylamine) until the theoretical endpoint wasreached after approximately 3-4 hours. The reaction mixture was thencooled to 50-60° C. and a calculated amount of 1.335 molar equivalent ofa blocking agent (e.g., 2-pentanone oxime or 2-butanone oximes orothers), (an amount that molar equivalent of the residual freeisocyanate (NCO) in the pre-polymer), in N-alkyl caprolactam or blendswas added and monitored via IR spectroscopy until no residual NCOcontent was present. This blocked prepolymer was subject to aneutralization reaction with 1.0 molar equivalent of a neutralizer(trimethylamine or ammonia) at 50-60° C. for one hour and then dispersedin deionized water.

While this disclosure has been described as relative to exemplarydesigns, the present disclosure may be further modified within thespirit and scope of this disclosure. Further, this application isintended to cover such departures from the present disclosure as comewithin known or customary practice in the art to which this disclosurepertains.

1. A method of forming a polyurethane dispersion comprising the stepsof: forming a polyurethane pre-polymer from a polymeric diol and atleast one of a polyisocyanate and a diisocyanate, and a hydrophilicagent, the polyurethane pre-polymer dissolved in water and a processingsolvent comprising N-ethyl caprolactam; adding at least one base to thepre-polymer; and dispersing the pre-polymer in water to form apolyurethane dispersion, the polyurethane dispersion comprising N-ethylcaprolactam.
 2. The method of claim 1, wherein the N-ethyl caprolactamis present in an amount from 1 wt. % to 10 wt. %, based on a totalweight of the polyurethane dispersion.
 3. The method of claim 1, furthercomprising, after the dispersing step, the additional step offormulating the polyurethane dispersion into a coating compositioncomprising a resin and N-ethyl caprolactam.
 4. The method of claim 1,further comprising, after the dispersing step, the additional step ofadding a coalescing agent to the polyurethane dispersion, the coalescingagent comprising N-ethyl caprolactam.
 5. The method of claim 1, whereinthe polymeric diol includes at least one polymeric diol selected from apolyether polyol, a polyester polyol, a polycarbonate polyol, apolyamide polyol, an acrylic polyol and combinations thereof.
 6. Themethod of claim 1, wherein the at least one of the polyisocyanate andthe diisocyanate is diisocyanate, which includes at least onediisocyanate selected from an aliphatic diisocyanate and an aromaticdiisocyanate and combinations thereof.
 7. The method of claim 1,characterized in that the hydrophilic agent is selected from the groupconsisting of dimethylol propionic acid, dimethylol butanoic acid andcombinations thereof.
 8. The method of claim 7, wherein the hydrophilicagent is dimethylol propionic acid.
 9. The method of claim 1, whereinthe at least one base is an amine.